1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to a method and an apparatus for transmitting reference signals at a base station (BS) for location based service in a wireless communication system, and a method and an apparatus for measuring a location of a user equipment (UE) by receiving the signals.
2. Discussion of the Related Art
Methods for measuring the location of a user equipment (UE) can be generally divided into two methods. The first method is a downlink (DL)-based location measurement method that measures the location of a user equipment (UE) on the basis of a DL signal transmitted from a base station (BS) to a user equipment (UE), and the second method is an uplink (UL)-based location measurement method that measures the location of a UE on the basis of a UL signal transmitted from the UE to the BS. In case of the DL-based location measurement, the UE receives DL signals from a plurality of cells, and measures location-associated parameters such as a time delay of the UL signals. In contrast, in case of the UL-based location measurement, the BS measures location-associated parameters such as a time delay of UL signals transmitted from the UE to the BS and neighbor BSs. That is, the UE geographical location can be calculated by measuring either a delay time of signals transmitted from several cells to the UE or a delay time of signals transmitted from the UE to several cells. Therefore, there are needed a plurality of signals to measure the UE location. Based on the above-mentioned description, although there are a variety of methods for calculating the UE location, a Time Difference of Arrival (TDOA) or Time Of Arrival (DOA) method has been generally used.
FIG. 1 is a conceptual view illustrating a downlink TDOA scheme for measuring a location of a user equipment.
Referring to FIG. 1, the downlink TDOA scheme is to measure a location of a user equipment by using the difference in timing of signals transmitted from respective cells to the user equipment. The user equipment measures a delay time of each signal received from each cell and reports the measured delay times to a serving cell or an anchor cell. The serving cell measures a location of the corresponding user equipment by using the reported delay times.
Meanwhile, in order to provide a communication service of high quality, the need of a location measurement scheme for determining a location of a user equipment within a network and/or locations of entities related to the user equipment more exactly has been increased. In this respect, an advanced method for determining a location while minimizing an effect on a structure of an existing radio frame should be provided.